Electrosurgical systems and methods for the removal of pacemaker leads

ABSTRACT

The present invention is directed to systems, methods and apparatus for removing implanted objects from a patient&#39;s body, particularly implanted endocardial or epicardial pacemaker leads and transvenous defibrillation leads from a patient&#39;s heart. In one aspect of the invention, an electrosurgical catheter is advanced to a position within the thoracic cavity adjacent a portion of a pacemaker lead that is affixed to heart tissue. Preferably, the catheter is advanced over the pacemaker lead, i.e., using the pacemaker lead as a guidewire, to facilitate this positioning step. Once the distal end of the catheter reaches a blockage, or a portion of the lead that is attached to fibrous scar tissue, a high frequency voltage difference is applied between one or more electrode terminal(s) at the distal end of the catheter and one or more return electrode(s) to remove the scar tissue around the lead. The catheter is then advanced further along the lead until it reaches another blockage caused by fibrous scar tissue, and the process is continued until the catheter reaches the distal tip of the lead in the myocardium. At this point, the distal tip may be severed from the rest of the lead, or pulled out of the myocardial tissue in a conventional manner. The scar tissue around the pacemaker lead is precisely ablated before removing the lead, which minimizes or eliminates the risks associated with mechanical traction and countertraction, such as disruption of the heart wall, lead breakage with subsequent migration and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of ProvisionalApplication No. 60/057,691 filed Aug. 27, 1997, the complete disclosureof which is incorporated herein by reference.

The present invention is related to commonly assigned co-pendingProvisional Application Nos. 60/062,997 and 60/062,996 both filed onOct. 23, 1997, application Ser. No. 08/942,580 filed Oct. 2, 1997, U.S.application Ser. No. 08/753227, filed on Nov. 22, 1996, U.S. applicationSer. No. 08/687792, filed on Jul. 18, 1996, and U.S. Pat. No. 5,697,909,filed on May 10, 1994, which was a continuation-in-part of applicationSer. No. 08/059,681, filed on May 10, 1993, which was acontinuation-in-part of application Ser. No. 07/958,977, filed on Oct.9, 1992 which was a continuation-in-part of application Ser. No.07/817,575, filed on Jan. 7, 1992, the complete disclosures of which areincorporated herein by reference for all purposes. The present inventionis also related to commonly assigned U.S. Pat. Nos. 5,683,366, and5,697,281 the complete disclosures of which are incorporated herein byreference for all purposes.

BACKGROUND OF THE INVENTION

The present invention is directed to electrosurgical systems, apparatusand methods for removing an implanted object from a patient's body, andspecifically to systems and methods for the removal of implantedendocardial or epicardial pacemaker leads or transvenous defibrillationleads from a patient's heart and the venous paths thereto.

Various types of pacemaker leads and their electrodes are introducedinto different chambers of the heart, including the right ventricle,right atrial appendage, the atrium and the coronary sinus, although themajority of pacemaker leads are implanted in the right ventricle orappendage thereof. These flexible leads provide an electrical pathwaybetween a pulse generator, connected to the proximal end of the lead,and the heart tissue, which is in contact with the distal end orelectrode of the lead. Electrical pulses emitted by the pacemaker travelthrough the pacemaker lead and stimulate the heart to restore healthyheart rhythms for patient's whose hearts are beating irregularly.

Pacemaker leads usually comprise an insulating sleeve that contains acoiled conductor having an electrode tip at the distal end. Thiselectrode tip is often placed in contact with the endocardial ormyocardial tissue by passage through a venous access, such as thesubclavian vein or one of its tributaries, which leads to theendocardial surface of the heart chambers. The electrode tip is held inplace within the trabeculations of myocardial tissue. The distal ends ofmany available leads include flexible tines, wedges or finger-likeprojections which project radially outward to help prevent dislodgmentof the lead tip from the cardial tissue.

Once an endocardial lead is implanted within a heart chamber, the body'sreaction to its presence furthers its fixation within the heart. Shortlyafter placement, blood clots form about the flanges or tines due toenzymes released in response to the irritation of the cardial tissuecaused by the electrode tip. Over time, fibrous scar tissue eventuallyforms over the distal end, usually in three to six months. In addition,fibrous scar tissue often forms, at least in part, over the insulatorsleeve within the venous system and the heart chamber.

Endocardial leads occasionally malfunction, due to a variety of reasons,including lead block, insulation breaks, breakage of the inner helicalcoil conductor, etc. In addition, it is sometimes desirable toelectronically stimulate different portions of the heart than that beingstimulated with leads already in place. Due to these and other factors,a considerable number of patients may eventually have more than one, andsometimes as many as four or five, unused leads in their venous systemsand heart. These unused leads often develop complications, such asinfection, septicemia, or endocarditis. In addition, unused leads mayentangle over time, thereby increasing the likelihood of blood clotformation, which may embolize to the lung and produce severecomplications or even fatality. Further, the presence of unused leads inthe venous pathway and inside the heart may cause considerabledifficulty in the positioning and attachment of new endocardial leads inthe heart.

Conventional techniques for removing unused pacemaker leads are alsoassociated with serious risks. Standard mechanical traction and, moreoften, intravascular mechanical countertraction are the methods mostcommonly used at present (notably the system manufactured by CookPacemaker Corporation). External mechanical traction involves graspingthe proximal end of the lead and pulling. This process is repeateddaily, usually a few millimeters of the lead are removed from thepatient each day, with progress monitored by chest radiography. Internalmechanical traction is accomplished by exerting traction (manual orsustained) on the lead via a snare, forceps or other retrieval catheterthat has grasped the lead within the venous system. These techniques,however, can cause disruption of the heart wall prior to release of theaffixed lead tip, causing fatality, or other complications, such as leadbreakage with subsequent migration, myocardial avulsion or avulsion of atricuspid valve leaflet. Moreover, lead removal may further be preventedby a channel of fibrotic scar tissue and endothelium surrounding theouter surface of the lead body or insulator sleeve at least part wayalong the venous pathway. Such channel scar tissue inhibits withdrawalof the lead because it is encased within the scar tissue. Continualpulling or twisting of the proximal free end of the lead could causerupturing of the right atrial wall or right ventricular wall.

Intravascular countertraction is accomplished by applying traction onthe lead while countering this traction by the circumference of dilatorsheaths advanced over the lead. While maintaining sufficient traction onthe lead to guide the sheaths, a pair of sheaths is advanced over thelead toward the myocardium to dislodge scar tissue from the lead. Ifinsufficient tension is placed on the lead, however, the method is nolonger countertraction but reduced to external traction with theaforementioned risks. In addition, misdirected countertraction along thelead body may tear the vein or heart wall.

In an effort to overcome some of the problems associated with mechanicaltraction and intravascular countertraction lead removal methods, lasershave been developed for extracting pacemaker leads. In some of thesetechniques, catheters having laser fibers at their distal end areadvanced over the pacemaker lead to the site of attachment. The laserfibers are then energized to separate the lead from the fibrous scartissue. These devices are described in U.S. Pat. Nos. 5,423,806,5,643,251, 5,514,128 and 5,484,433. The standard laser light source forthese devices is the xenon-chloride excimer laser, which is commerciallyavailable from Spectranetics Corporation of Colorado Springs, Col.

Conventional electrosurgery methods have not been successful in removingpacemaker leads. One of the factors which appears to create the greatestimpediment to electrosurgical removal of pacemaker leads is scar tissue.Scar tissue exhibits much lower thermal conductivity and electricalconductivity than normal (e.g., myocardial) tissue. Since conventionalelectrosurgery generally relies on the conduction of electrical currentsthrough the target tissue being cut or vaporized, conventionalelectrosurgery has failed to remove this scar tissue. In fact, previousattempts to use conventional electrosurgery methods to remove pacemakerleads have resulted in current flow and thermal effects in the “healthy”tissue surrounding the scar tissue mass, but not in the scar tissue massitself. As a result, the targeted scar tissue was not affected and thelead was not removable.

SUMMARY OF THE INVENTION

The present invention is directed to systems, methods and apparatus forremoving implanted objects from a patient's body, particularly implantedobjects attached to fibrous scar tissue. The systems and methods of thepresent invention are particularly useful for removing implantedendocardial or epicardial pacemaker leads or transvenous defibrillationleads from a patient's heart.

Methods of the present invention comprise positioning one or moreelectrode terminal(s) adjacent an implanted object attached to tissueand applying a sufficient high frequency voltage difference between theelectrode terminal(s) and one or more return electrode(s) to detach theimplanted object from the tissue. The high frequency voltage istypically sufficient to ablate or remove a portion of the tissue betweenthe implanted object and the remaining tissue so that the implantedobject can then be removed without pulling or tearing the patient'stissue. In preferred embodiments, an electrically conductive fluid, suchas isotonic saline or conductive gas, is delivered to the target sitearound the pacemaker lead to substantially surround the electrodeterminal(s) with the fluid. Alternatively, a more viscous fluid, such asan electrically conductive gel, may be delivered or applied directly tothe target site such that the electrode terminal(s) are immersed withinthe gel during the procedure. In both embodiments, high frequencyvoltage is applied between the electrode terminal(s) and one or morereturn electrode(s) to remove at least a portion of the tissue.

In one aspect of the invention, an electrosurgical catheter is advancedto a position within the thoracic cavity adjacent a portion of apacemaker lead that is affixed to heart tissue. Preferably, the catheteris advanced over the pacemaker lead, i.e., using the pacemaker lead as aguidewire, to facilitate this positioning step. Once the distal end ofthe catheter reaches a blockage, or a portion of the lead that isattached to fibrous scar tissue, a high frequency voltage difference isapplied between one or more electrode terminal(s) at the distal end ofthe catheter and one or more return electrode(s) to remove the scartissue around the lead. Depending on the configuration of the distal endof the catheter, the electrode terminal(s) may be rotated, oscillated orotherwise manipulated to facilitate the removal of tissue between thelead and the heart. The catheter is then advanced further along the leaduntil it reaches another blockage caused by fibrous scar tissue, and theprocess is continued until the catheter reaches the distal tip of thelead in the myocardium. At this point, the distal tip may be severedfrom the rest of the lead, or pulled out of the myocardial tissue in aconventional manner. Alternatively, the catheter may be energized andadvanced through the myocardial tissue to form an annular channel arounda portion of the distal tip. If the distal tip includes flanges ortines, these tines may be severed with the electrical energy, and theremainder of the distal tip removed from the myocardial tissue.

In a specific configuration, the fibrous scar tissue is removed bymolecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the electrodeterminal(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel or saline) between the electrode terminal(s) and the tissue.Within the vaporized fluid, a ionized plasma is formed and chargedparticles (e.g., electrons) are accelerated towards the tissue to causethe molecular breakdown or disintegration of several cell layers of thetissue. This molecular dissociation is accompanied by the volumetricremoval of the tissue. The short range of the accelerated chargedparticles within the plasma layer confines the molecular dissociationprocess to the surface layer to minimize damage and necrosis to theunderlying tissue. This process can be precisely controlled to effectthe volumetric removal of tissue as thin as 10 to 150 microns withminimal heating of, or damage to, surrounding or underlying tissuestructures. A more complete description of this phenomena is describedin commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure ofwhich is incorporated herein by reference.

The present invention offers a number of significant advantages overcurrent techniques for removing pacemaker leads. For one thing, the scartissue around the pacemaker lead is precisely ablated before removingthe lead, which minimizes or eliminates the risks associated withmechanical traction and countertraction, such as disruption of the heartwall, lead breakage with subsequent migration and the like. In addition,the ability to precisely control the volumetric removal of tissueresults in tissue ablation or removal that is very defined, consistentand predictable. The shallow depth of tissue heating also helps tominimize or completely eliminate thermal damage to the heart. Inparticular, since the mechanism for removing or ablating the scar tissuedoes not rely primarily on electrical current flow through the scartissue, the low electrical conductivity of the scar tissue (relative tothe adjacent heart tissue) does not effect the removal of this tissue.In addition, since the electrical current primarily flows back to thereturn electrode through the electrically conductive fluid, current flowinto healthy heart tissue is minimized. Moreover, since the presentinvention allows for the use of electrically conductive fluid (contraryto prior art bipolar and monopolar electrosurgery techniques), isotonicsaline may be used during the procedure. Saline is the preferred mediumfor irrigation because it has the same concentration as the body'sfluids and, therefore, is not absorbed into the body as much as otherfluids.

Apparatus of the present invention comprise a catheter shaft having aflexible body with a proximal end portion and a distal end portionhaving a distal opening. The catheter shaft has an inner lumen coupledto the distal opening and sized to accommodate a pacemaker lead, usuallyabout 0.2 to 10 mm diameter and preferably about 0.5 to 5 mm indiameter. The catheter body has one or more electrode terminal(s) on theshaft at the distal end portion, and a connector extending through thebody for coupling the electrode terminal(s) to a source of highfrequency electrical energy.

The apparatus will preferably further include one or more fluid deliveryelement(s) for delivering electrically conducting fluid to the electrodeterminal(s) and the target site. The fluid delivery element(s) may belocated on the catheter, e.g., one or more fluid lumen(s) or tube(s), orthey may be part of a separate instrument. Alternatively, anelectrically conducting gel or spray, such as a saline electrolyte orother conductive gel, may be applied the target site. In thisembodiment, the apparatus may not have a fluid delivery element. In bothembodiments, the electrically conducting fluid will preferably generatea current flow path between the electrode terminal(s) and one or morereturn electrode(s). In an exemplary embodiment, the return electrode(s)are located on the catheter and spaced a sufficient distance from theelectrode terminal(s) to substantially avoid or minimize currentshorting therebetween and to shield the return electrode(s) from tissueat the target site. Alternatively, the return electrode(s) may comprisea dispersive pad located on the outer surface of the patient (i.e., amonopolar modality).

In a specific configuration, the apparatus includes a plurality ofelectrically isolated electrode terminals extending from the distal endof the catheter shaft. The electrode terminals are each mounted withinan electrically insulating support member, and spaced peripherallyaround the distal opening of the catheter body. In these embodiments,the catheter may include a single, annular return electrode locatedproximal of the distal opening, or a plurality of electrode terminalsmounted to the support members proximal of the electrode terminals. Thelatter embodiment has the advantage that the electric currents areconfined to a distal region of the catheter body, which may facilitateadvancement of the catheter through fibrous scar tissue. In thisembodiment, the catheter body also includes one or more fluid deliverylumens spaced peripherally around the central lumen for deliveringelectrically conductive fluid to the electrode terminals. In addition,the catheter body will preferably include one or more suction lumensspaced peripherally around the central lumen, and suitably coupled to anexternal suction source for aspirating fluid, tissue and/or gaseousproducts of ablation (e.g., non-condensible gases) from the target site.

In one embodiment, the catheter includes a lateral port, opening or slitproximal to the distal end of the catheter (typically about 0.5 to 10cm), and sized for receiving the pacemaker lead therethrough. In thisembodiment, the pacemaker lead is loaded through the distal opening intothe inner lumen of the catheter, and out through the lateral port sothat the lead only extends through a distal end portion of the catheterbody. This side port loading feature makes it easier to advance thecatheter body over the pacemaker lead, and provides the physician withmore control of the distal end portion. For example, this enhancedcontrol allows the physician to rotate the distal end of the catheterrelative to the pacemaker lead and the fibrous scar tissue to facilitatethe removal of an annular channel of scar tissue around the lead (e.g.,the electrode terminals are energized and rotated to ablate or remove anannular channel of tissue). In this embodiment, the connectors for theelectrode terminal(s) and the return electrode(s) are preferably flattape wires that extend around the periphery of the distal end portion,and around the lateral port to the proximal end of the catheter body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional pacemaker lead incorporating tines toanchor the tip of the pacemaker lead into the heart wall;

FIG. 2 is an exploded, cross-sectional view of the tip of the pacemakerlead;

FIG. 3 is a perspective view of an electrosurgical catheter system forremoving implanted objects within a patient's body;

FIG. 4 illustrates one embodiment of an electrosurgical catheter for theremoval of pacemaker leads according to the present invention;

FIG. 5 is a distal end view of the catheter of FIG. 4;

FIGS. 6 and 7 are perspective and cross-sectional views of a flexcircuit for coupling a plurality of electrode terminals within thecatheter of FIG. 4 to a high frequency power supply;

FIG. 8A is a perspective view of a distal portion of a second embodimentof an electrosurgical catheter according to the present invention;

FIG. 8B illustrates a third embodiment of the catheter, incorporating apair of return electrodes;

FIG. 9 is a cross sectional view of the electrosurgical catheter takenalong lines 9—9 in FIG. 8A;

FIG. 10 illustrates the proximal portion of the electrosurgical catheterof FIG. 8A;

FIG. 11 is a cross-sectional view of the catheter taken along lines11—11 in FIG. 10;

FIG. 12 illustrates one of the electrode assemblies of theelectrosurgical catheter according to the embodiment of FIG. 8B;

FIG. 13 illustrates an alternative embodiment of an electrode assemblyincorporating a central fluid lumen for delivery of electricallyconductive fluid to the target site;

FIGS. 14A and 14B illustrates a fourth embodiment of an electrosurgicalcatheter incorporating a retractable safety sheath for shielding thepatient from the electrode assemblies;

FIG. 15 illustrates a fifth embodiment of an electrosurgical catheterincorporating a lateral port for loading a pacemaker lead;

FIGS. 16A and 16B are transverse and longitudinal cross-sectional views,respectively, of a sixth embodiment of the distal ablation region of thecatheter;

FIGS. 17A and 17B are transverse and longitudinal cross-sectional views,respectively, of a seventh embodiment of the distal ablation region ofthe catheter;

FIGS. 18A and 18B are transverse and longitudinal cross-sectional views,respectively, of an eighth embodiment of the distal ablation region ofthe catheter;

FIGS. 19A and 19B are transverse and longitudinal cross-sectional views,respectively, of a ninth embodiment of the distal ablation region of thecatheter;

FIGS. 20A and 20B are transverse and longitudinal cross-sectional views,respectively, of a tenth embodiment of the distal ablation region of thecatheter;

FIGS. 21A and 21B are transverse and longitudinal cross-sectional views,respectively, of an eleventh embodiment of the distal ablation region ofthe catheter;

FIG. 22 is a schematic view of the patient's heart and a portion of thecardiovascular system, illustrating a method of removing a pacemakerlead by translating an electrosurgical catheter over the lead;

FIG. 23 is an exploded view of the distal portion of an electrosurgicalcatheter, illustrating a method of removing tissue surrounding thepacemaker lead to separate the lead from the heart; and

FIG. 24 is an exploded view of the distal portion of an electrosurgicalcatheter, illustrating a method of removing tissue surrounding the tipof a pacemaker lead.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices, systems and methods whichemploy high frequency electrical energy to remove or ablate tissueattached to implanted objects within the body. The systems and methodsof the present invention are particularly useful for removing implantedendocardial or epicardial pacemaker leads or transvenous defibrillationleads from a patient's heart. In addition to pacemaker lead removal, thepresent invention may be used in body lumens, e.g., for removingatheromatous material which partially or fully occludes the body lumen,such as a blood vessel or for removing stents or other implantedobjects. Moreover, other body lumens that may be treated by the methodand apparatus of the present invention include the urinary tract (whichfor example may be occluded by an enlarged prostrate in males), thefallopian tubes (which may be occluded and cause infertility), and thelike. In fact, the methods and apparatus disclosed herein may be used ina wide variety of procedures, including open procedures, intravascularprocedures, urology, laparoscopy, arthroscopy, thoracoscopy or othercardiac procedures, dermatology, orthopedics, gynecology,otorhinolaryngology, spinal and neurologic procedures, oncology and thelike. For convenience, the remaining disclosure will be directedspecifically to the removal of pacemaker leads from the heart.

In the present invention, high frequency (RF) electrical energy isapplied to one or more electrode terminals (usually in the presence ofelectrically conductive fluid) to remove and/or modify the structure oftissue structures. Depending on the specific procedure, the presentinvention may be used to: (1) volumetrically remove tissue (i.e., ablateor effect molecular dissociation of the tissue structure); (2) cut orresect tissue; (3) vaporize, cauterize or desiccate tissue and/or (4)coagulate and seal severed blood vessels.

In the preferred method of the present invention, tissue around animplanted object, such as fibrous scar tissue, is volumetrically removedor ablated. In this procedure, a high frequency voltage difference isapplied between one or more electrode terminal(s) and one or more returnelectrode(s) to develop high electric field intensities in the vicinityof the target tissue. The high electric field intensities lead toelectric field induced molecular breakdown of target tissue throughmolecular dissociation (rather than thermal evaporation orcarbonization). Applicant believes that the tissue structure isvolumetrically removed through molecular disintegration of largerorganic molecules into smaller molecules and/or atoms, such as hydrogen,oxides of carbon, hydrocarbons and nitrogen compounds. This moleculardisintegration completely removes the tissue structure, as opposed todehydrating the tissue material by the removal of liquid within thecells of the tissue, as is typically the case with electrosurgicaldesiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the electrode terminal(s) inthe region between the distal tip of the electrode terminal(s) and thetarget tissue. The electrically conductive fluid may be a liquid, suchas isotonic saline or blood, delivered to the target site, or a viscousfluid, such as a gel, applied to the target site. Since the vapor layeror vaporized region has a relatively high electrical impedance, itincreases the voltage differential between the electrode terminal tipand the tissue and causes ionization within the vapor layer due to thepresence of an ionizable species (e.g., sodium when isotonic saline isthe electrically conducting fluid). This ionization, under optimalconditions, induces the discharge of energetic electrons and photonsfrom the vapor layer and to the surface of the target tissue. Thisenergy may be in the form of energetic photons (e.g., ultravioletradiation), energetic particles (e.g., electrons) or a combinationthereof. A more detailed description of this phenomena, termedCoblation™ can be found in commonly assigned U.S. Pat. No. 5,683,366 thecomplete disclosure of which is incorporated herein by reference.

The present invention applies high frequency (RF) electrical energy inan electrically conducting fluid environment to remove (i.e., resect,cut or ablate) a tissue structure, and to seal transected vessels withinthe region of the target tissue. The present invention is particularlyuseful for sealing larger arterial vessels, e.g., on the order of 1 mmor greater. In some embodiments, a high frequency power supply isprovided having an ablation mode, wherein a first voltage is applied toan electrode terminal sufficient to effect molecular dissociation ordisintegration of the tissue, and a coagulation mode, wherein a second,lower voltage is applied to an electrode terminal (either the same or adifferent electrode) sufficient to achieve hemostasis of severed vesselswithin the tissue. In other embodiments, an electrosurgical probe isprovided having one or more coagulation electrode(s) configured forsealing a severed vessel, such as an arterial vessel, and one or moreelectrode terminals configured for either contracting the collagenfibers within the tissue or removing (ablating) the tissue, e.g., byapplying sufficient energy to the tissue to effect moleculardissociation. In the latter embodiments, the coagulation electrode(s)may be configured such that a single voltage can be applied to coagulatewith the coagulation electrode(s), and to ablate with the electrodeterminal(s). In other embodiments, the power supply is combined with thecoagulation probe such that the coagulation electrode is used when thepower supply is in the coagulation mode (low voltage), and the electrodeterminal(s) are used when the power supply is in the ablation mode(higher voltage).

The present invention is also useful for removing or ablating tissuearound nerves, such as spinal, visceral or cranial nerves, e.g., theolfactory nerve on either side of the nasal cavity, the optic nervewithin the optic and cranial canals, the palatine nerve within the nasalcavity, soft palate, uvula and tonsil, etc. One of the significantdrawbacks with prior art mechanical cutters and lasers is that thesedevices do not differentiate between the target tissue and thesurrounding nerves or bone. Therefore, the surgeon must be extremelycareful during these procedures to avoid damage to the bone or nerveswithin and around the nasal cavity. In the present invention, theCoblation™ process for removing tissue results in extremely small depthsof collateral tissue damage as discussed above. This allows the surgeonto remove tissue close to a nerve without causing collateral damage tothe nerve fibers. A more complete description of this phenomena can befound in co-pending U.S. Patent Application entitled “Systems andMethods for Endoscopic Sinus Surgery”, filed Dec. 15, 1997, the completedisclosure of which is incorporated herein by reference.

In the method of the present invention, one or more electrode terminalsare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the electrode terminals and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the electrode terminals may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent probe may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

The electrosurgical instrument will comprise a shaft having a proximalend and a distal end which supports one or more electrode terminal(s).The shaft may assume a wide variety of configurations, with the primarypurpose being to mechanically support one or more electrode terminal(s)and permit the treating physician to manipulate the electrode(s) from aproximal end of the shaft. Usually, an electrosurgical probe shaft willbe a narrow-diameter rod or tube, more usually having dimensions whichpermit it to be introduced into a body cavity, such as the thoraciccavity, through an associated trocar or cannula in a minimally invasiveprocedure, such as arthroscopic, laparoscopic, thoracoscopic, and otherendoscopic procedures. Thus, the probe shaft will typically have alength of at least 5 cm for open procedures and at least 10 cm, moretypically being 20 cm, or longer for endoscopic procedures. The probeshaft will typically have a diameter of at least 1 mm and frequently inthe range from 1 to 10 mm.

The electrosurgical probe may be delivered percutaneously(endoluminally) to the ventricular cavity of the heart by insertionthrough a conventional or specialized guide catheter, or the inventionmay include a catheter having an active electrode array integral withits distal end. The catheter shaft may be rigid or flexible, withflexible shafts optionally being combined with a generally rigidexternal tube for mechanical support. Flexible shafts may be combinedwith pull wires, shape memory actuators, and other known mechanisms foreffecting selective deflection of the distal end of the shaft tofacilitate positioning of the electrode or electrode array. The shaftwill usually include a plurality of wires or other conductive elementsrunning axially therethrough to permit connection of the electrode orelectrode array and the return electrode to a connector at the proximalend of the shaft. The catheter may include a guide wire for guiding thecatheter to the target site, or the catheter may comprise a steerableguide catheter. In the preferred configuration, the pacemaker lead willbe used as the guide wire, as discussed below. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter.

The electrode terminal(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft, e.g., a catheter body. The return electrode may belocated on the catheter body, on another instrument, on the externalsurface of the patient (i.e., a dispersive pad), or the return electrodemay be the lead tip itself. The likely presence of scar tissuesurrounding the lead tip, however, will usually limit use of the lead asthe return electrode due to inadequate current flow through the smallexposed area of lead at the tip, and the potentially high electricalimpedance of the surrounding scar tissue. In addition, the closeproximity of the heart makes a bipolar design more preferable (i.e., nodispersive pad). Accordingly, the return electrode is preferably eitherintegrated with the catheter body, or another instrument located inclose proximity to the distal end of the catheter body. The proximal endof the catheter will include the appropriate electrical connections forcoupling the return electrode(s) and the electrode terminal(s) to a highfrequency power supply, such as an electrosurgical generator.

In the representative embodiment, the catheter will have an internallumen sized to accommodate the pacemaker lead, so that the catheter canbe advanced over the lead to the fibrous scar tissue. The diameter ofthe internal lumen will vary according to the pacemaker lead diameter,which typically range in diameter from about 0.2 to 10.0 mm, usually 0.5to 5.0 mm, often about 1.1 to 3.3 mm. Of course, the catheter of thepresent invention may be modified to accommodate newly designedpacemaker leads (e.g., with larger or small diameters). The internallumen may extend the entire length of the catheter, or only partwayalong the length of the catheter. In the latter embodiment, the catheterwill include a side port or opening so that the pacemaker lead can befed through the side port in a rapid exchange procedure to advance thecatheter along the lead. In order to provide maximum torque control, itmay be preferable to insert the distal end of the catheter over theentire length of pacemaker lead rather than limiting the “lead followinglumen” within the distal end to a relatively short length (e.g., 10 cm)from the working end of the catheter.

The current flow path between the electrode terminal(s) and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, or a gas, such as argon). The conductive gel may alsobe delivered to the target site to achieve a slower more controlleddelivery rate of conductive fluid. In addition, the viscous nature ofthe gel may allow the surgeon to more easily contain the gel around thetarget site (e.g., rather than attempting to contain isotonic saline). Amore complete description of an exemplary method of directingelectrically conducting fluid between the active and return electrodesis described in U.S. Pat. No. 5,697,281, previously incorporated hereinby reference. Alternatively, the body's natural conductive fluids, suchas blood, may be sufficient to establish a conductive path between thereturn electrode(s) and the electrode terminal(s), and to provide theconditions for establishing a vapor layer, as described above.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensible gaseousproducts of ablation. For example, in procedures in and around theheart, or within blood vessels, it may be desirable to aspirate thefluid so that it does not flow downstream. In addition, it may bedesirable to aspirate small pieces of tissue that are not completelydisintegrated by the high frequency energy, or other fluids at thetarget site, such as blood, mucus, the gaseous products of ablation,etc. Accordingly, the system of the present invention will usuallyinclude one or more suction lumen(s) in the probe, or on anotherinstrument, coupled to a suitable vacuum source for aspirating fluidsfrom the target site.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath or the like.This embodiment has the advantage of ensuring that the conductive fluid,tissue fragments or ablation products do not flow into the heart orlungs. In addition, it may be desirable to limit the amount of suctionto limit the undesirable effect suction may have on hemostasis ofsevered blood vessels within heart tissue.

The present invention may use a single active electrode terminal or anarray of electrode terminals spaced around the distal surface of acatheter or probe. In the latter embodiment, the electrode array usuallyincludes a plurality of independently current-limited and/orpower-controlled electrode terminals to apply electrical energyselectively to the target tissue while limiting the unwanted applicationof electrical energy to the surrounding tissue and environment resultingfrom power dissipation into surrounding electrically conductive liquids,such as blood, normal saline, and the like. The electrode terminals maybe independently current-limited by isolating the terminals from eachother and connecting each terminal to a separate power source that isisolated from the other electrode terminals. Alternatively, theelectrode terminals may be connected to each other at either theproximal or distal ends of the catheter to form a single wire thatcouples to a power source.

In one configuration, each individual electrode terminal in theelectrode array is electrically insulated from all other electrodeterminals in the array within said probe and is connected to a powersource which is isolated from each of the other electrode terminals inthe array or to circuitry which limits or interrupts current flow to theelectrode terminal when low resistivity material (e.g., blood,electrically conductive saline irrigant or electrically conductive gel)causes a lower impedance path between the return electrode and theindividual electrode terminal. The isolated power sources for eachindividual electrode terminal may be separate power supply circuitshaving internal impedance characteristics which limit power to theassociated electrode terminal when a low impedance return path isencountered. By way of example, the isolated power source may be a userselectable constant current source. In this embodiment, lower impedancepaths will automatically result in lower resistive heating levels sincethe heating is proportional to the square of the operating current timesthe impedance. Alternatively, a single power source may be connected toeach of the electrode terminals through independently actuatableswitches, or by independent current limiting elements, such asinductors, capacitors, resistors and/or combinations thereof. Thecurrent limiting elements may be provided in the probe, connectors,cable, controller or along the conductive path from the controller tothe distal tip of the probe. Alternatively, the resistance and/orcapacitance may occur on the surface of the active electrode terminal(s)due to oxide layers which form selected electrode terminals (e.g.,titanium or a resistive coating on the surface of metal, such asplatinum).

The tip region of the probe may comprise many independent electrodeterminals designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual electrode terminal andthe return electrode to a power source having independently controlledor current limited channels. The return electrode(s) may comprise asingle tubular member of conductive material proximal to the electrodearray at the tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the probe may comprise an array of return electrodes atthe distal tip of the probe (together with the active electrodes) tomaintain the electric current at the tip. The application of highfrequency voltage between the return electrode(s) and the electrodearray results in the generation of high electric field intensities atthe distal tips of the electrode terminals with conduction of highfrequency current from each individual electrode terminal to the returnelectrode. The current flow from each individual electrode terminal tothe return electrode(s) is controlled by either active or passive means,or a combination thereof, to deliver electrical energy to thesurrounding conductive fluid while minimizing energy delivery tosurrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the electrode terminal(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. The tissue volume over whichenergy is dissipated (i.e., a high current density exists) may beprecisely controlled, for example, by the use of a multiplicity of smallelectrode terminals whose effective diameters or principal dimensionsrange from about 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm,and more preferably from about 1 mm to 0.1 mm. Electrode areas for bothcircular and non-circular terminals will have a contact area (perelectrode terminal) below 25 mm², preferably being in the range from0.0001 mm² to 1 mm², and more preferably from 0.005 mm² to 0.5 mm². Thecircumscribed area of the electrode array is in the range from 0.25 mm²to 75 mm², preferably from 0.5 mm² to 40 mm², and will usually includeat least two isolated electrode terminals, preferably at least fiveelectrode terminals, often greater than 10 electrode terminals and even50 or more electrode terminals, disposed over the distal contactsurfaces on the shaft. The use of small diameter electrode terminalsincreases the electric field intensity and reduces the extent or depthof tissue heating as a consequence of the divergence of current fluxlines which emanate from the exposed surface of each electrode terminal.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Activeelectrode surfaces can have areas in the range from 0.25 mm² to 75 mm²,usually being from about 0.5 mm² to 40 mm². The geometries can beplanar, concave, convex, hemispherical, conical, linear “in-line” arrayor virtually any other regular or irregular shape. Most commonly, theactive electrode(s) or electrode terminal(s) will be formed at thedistal tip of the electrosurgical probe shaft, frequently being planar,disk-shaped, or hemispherical surfaces for use in reshaping proceduresor being linear arrays for use in cutting. Alternatively oradditionally, the active electrode(s) may be formed on lateral surfacesof the electrosurgical probe shaft (e.g., in the manner of a spatula),facilitating access to certain body structures in endoscopic procedures.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the probe or handpiece to confine theelectrically conductive fluid to the region immediately surrounding theelectrode support. In addition, the shaft may be shaped so as to form acavity around the electrode support and the fluid outlet. This helps toassure that the electrically conductive fluid will remain in contactwith the electrode terminal(s) and the return electrode(s) to maintainthe conductive path therebetween. In addition, this will help tomaintain a vapor or plasma layer between the electrode terminal(s) andthe tissue at the treatment site throughout the procedure, which reducesthe thermal damage that might otherwise occur if the vapor layer wereextinguished due to a lack of conductive fluid. Provision of theelectrically conductive fluid around the target site also helps tomaintain the tissue temperature at desired levels.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe electrode terminal(s). The electrical conductivity of the fluid (inunits of milliSiemans per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm.

The voltage difference applied between the return electrode(s) and theelectrode terminal(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, morepreferably less than 350 kHz, and most preferably between about 100 kHzand 200 kHz. The RMS (root mean square) voltage applied will usually bein the range from about 5 volts to 1000 volts, preferably being in therange from about 10 volts to 500 volts depending on the electrodeterminal size, the operating frequency and the operation mode of theparticular procedure or desired effect on the tissue (i.e., contraction,coagulation or ablation). For removal of pacemaker leads attached toheart tissue, the voltage will usually be in the range of about 100 to300 Vrms. Typically, the peak-to-peak voltage will be in the range of 10to 2000 volts and preferably in the range of 20 to 500 volts and morepreferably in the range of about 40 to 450 volts (again, depending onthe electrode size, the operating frequency and the operation mode).

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular cardiac surgery, arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, open surgery or other endoscopicsurgery procedure. For cardiac procedures, the power source may have anadditional filter, for filtering leakage voltages at frequencies below100 kHz, particularly voltages around 60 kHz. A description of asuitable power source can be found in “SYSTEMS AND METHODS FORELECTROSURGICAL TISSUE AND FLUID COAGULATION”, filed on Oct. 23, 1997.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent electrode terminal, where the inductance of theinductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously in U.S. Pat.No. 5,697,909, the complete disclosure of which is incorporated hereinby reference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual electrode terminal in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said electrode terminal into the low resistance medium(e.g., saline irrigant or blood).

In yet another aspect of the invention, the control system is “tuned” sothat it will not apply excessive power to the blood (e.g., in theventricle), once it crosses the wall of the heart and enters the chamberof the left ventricle. This minimizes the formation of a thrombus in theheart (i.e., will not induce thermal coagulation of the blood). Thecontrol system may include an active or passive architecture, and willtypically include a mechanism for sensing resistance between a pair(s)of active electrodes at the distal tip, or between one or more activeelectrodes and a return electrode, to sense when the electrode array hasentered into the blood-filled chamber of the left ventricle.Alternatively, current limiting means may be provided to preventsufficient joulean heating in the lower resistivity blood to causethermal coagulation of the blood. In another alternative embodiment, anultrasound transducer at the tip of the probe can be used to detect theboundary between the wall of the heart and the blood filled leftventricle chamber, turning off the electrode array just as the probecrosses the boundary.

It should be clearly understood that the invention is not limited toelectrically isolated electrode terminals, or even to a plurality ofelectrode terminals. For example, the array of active electrodeterminals may be connected to a single lead that extends through thecatheter shaft to a power source of high frequency current.Alternatively, the catheter may incorporate a single electrode thatextends directly through the catheter shaft or is connected to a singlelead that extends to the power source. The active electrode(s) may haveball shapes (e.g., for tissue vaporization and desiccation), twizzleshapes (for vaporization and needle-like cutting), spring shapes (forrapid tissue debulking and desiccation), twisted metal shapes, annularor solid tube shapes or the like. Alternatively, the electrode(s) maycomprise a plurality of filaments, rigid or flexible brush electrode(s)(for debulking a tumor, such as a fibroid, bladder tumor or a prostateadenoma), side-effect brush electrode(s) on a lateral surface of theshaft, coiled electrode(s) or the like.

In one embodiment, an electrosurgical catheter or probe comprises asingle active electrode terminal that extends from an insulating member,e.g., ceramic, at the distal end of the shaft. The insulating member ispreferably a tubular structure that separates the active electrodeterminal from a tubular or annular return electrode positioned proximalto the insulating member and the active electrode. In anotherembodiment, the catheter or probe includes a single active electrodethat can be rotated relative to the rest of the catheter body, or theentire catheter may be rotated related to the lead. The single activeelectrode can be positioned adjacent the scar tissue and energized androtated as appropriate to remove this tissue.

FIGS. 1 and 2 illustrate a conventional endocardial pacemaker lead 10according to the present invention. As shown, the lead 10 typicallyincludes a lead shaft 12 with a proximal hub 16 for attachment to apulse generator (not shown), and a distal tip 22 that is embedded intothe myocardium of the heart (see FIGS. 11 and 12). Many conventionallead tips 22 include expanded diameters and/or flaring tines 24 toensure that the tip remains embedded in the myocardial tissue. Theseflaring tines 24 may require flared or deflectable electrodes (discussedin detail below) to extend the radius of the tissue cutting/ablationbeyond the diameter of the main catheter body.

Referring now to FIG. 3, a catheter system 50 for removing implantedobjects from the body, such as pacemaker leads, is illustrated accordingto the present invention. Catheter system 50 generally comprises anelectrosurgical catheter 60 connected to a power supply 80 by aninterconnecting cable 86 for providing high frequency voltage to atarget tissue and an irrigant reservoir or source 100 for providingelectrically conducting fluid to the target site. Catheter 60 generallycomprises an elongate, flexible shaft body 62 including a tissueremoving or ablating region 64 at the distal end of body 62. Theproximal portion of catheter 6 includes a multi-lumen fitment 114 (seealso FIGS. 6 and 7) which provides for interconnections between lumensand electrical leads within catheter 60 and conduits and cables proximalto fitment 114. By way of example, a catheter electrical connector 96 isremovably connected to a distal cable connector 94 which, in turn, isremovably connectable to generator 80 through connector 92. One or moreelectrically conducting lead wires (not shown) within catheter 60 extendbetween one or more active electrodes 63 at tissue ablating region 64and one or more corresponding electrical terminals (also not shown) incatheter connector 96 via active electrode cable branch 87. Similarly,one or more return electrodes 65 at tissue ablating region 64 arecoupled to a return electrode cable branch 89 of catheter connector 96by lead wires (not shown). Of course, a single cable branch 91 may beused for both active and return electrodes, as shown in FIG. 6.

Power supply 80 has an operator controllable voltage level adjustment 82to change the applied voltage level, which is observable at a voltagelevel display 84. Power supply 80 also includes a foot pedal 88 and acable 90 which is removably coupled to power supply 80 for remotelyadjusting the energy level applied to electrode terminals. In anexemplary embodiment, power supply 80 includes three such foot pedals(not shown), wherein the first foot pedal is used to place the powersupply into the “ablation” mode and the second foot pedal places powersupply 80 into the “coagulation” mode. The third foot pedal allows theuser to adjust the voltage level within the “ablation” mode. In theablation mode, a sufficient voltage is applied to the electrodeterminals to establish the requisite conditions for moleculardissociation of the tissue (i.e., vaporizing a portion of theelectrically conductive fluid, ionizing charged particles within thevapor layer and accelerating these charged particles against thetissue). As discussed above, the requisite voltage level for ablationwill vary depending on the number, size, shape and spacing of theelectrodes, the distance in which the electrodes extend from the supportmember, etc. Once the surgeon places the power supply in the “ablation”mode, voltage level adjustment 82 or the third foot pedal may be used toadjust the voltage level to adjust the degree or aggressiveness of theablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the coagulation mode, the power supply 80 applies a low enoughvoltage to the electrode terminals (or the coagulation electrode) toavoid vaporization of the electrically conductive fluid and subsequentmolecular dissociation of the tissue. The surgeon may automaticallytoggle the power supply between the ablation and coagulation modes byalternatively stepping on the foot pedals. This allows the surgeon toquickly move between coagulation and ablation in situ, without having toremove his/her concentration from the surgical field or without havingto request an assistant to switch the power supply. By way of example,as the surgeon is sculpting soft tissue in the ablation mode, the probetypically will simultaneously seal and/or coagulation small severedvessels within the tissue. However, larger vessels, or vessels with highfluid pressures (e.g., arterial vessels) may not be sealed in theablation mode. Accordingly, the surgeon can simply step on theappropriate foot pedal, automatically lowering the voltage level belowthe threshold level for ablation, and apply sufficient pressure onto thesevered vessel for a sufficient period of time to seal and/or coagulatethe vessel. After this is completed, the surgeon may quickly move backinto the ablation mode by stepping on a foot pedal. A specific design ofa suitable power supply for use with the present invention can be foundin provisional patent application entitled “SYSTEMS AND METHODS FORELECTROSURGICAL TISSUE AND FLUID COAGULATION”, filed Oct. 23, 1997,previously incorporated herein by reference.

Conductive fluid 30 is provided to tissue ablation region 64 of catheter60 via an internal lumen 68 (see FIG. 5) within catheter 60. Fluid issupplied to the lumen from the source along a conductive fluid supplyline 102 and a conduit 103, which is coupled to the inner catheter lumenat multi-lumen fitment 114. The source of conductive fluid (e.g.,isotonic saline) may be an irrigant pump system (not shown) or a simplegravity-driven supply, such as an irrigant reservoir 100 positionedseveral feet above the level of the patient and tissue ablating region64. A control valve 104 may be positioned at the interface of fluidsupply line 102 and conduit 103 to allow manual control of the flow rateof electrically conductive fluid 30. Alternatively, a metering pump orflow regulator may be used to precisely control the flow rate of theconductive fluid.

Catheter system 50 further includes an aspiration or vacuum system (notshown) to aspirate liquids and gases from the target. One or moreinternal suction lumens 130, 132 within catheter body 62 are suitablycoupled to a fluid tube 97 at the proximal end of catheter 60. Fluidtube 97, in turn, includes a connector 98 for coupling to a controllablesource of vacuum (not shown).

Referring now to FIGS. 4-7, one embodiment of a catheter 400 accordingto the present invention will now be described. As shown in FIG. 4,catheter 400 includes a flexible catheter body 402 coupling a proximalhandle 404 to a distal ablation region 406. Distal ablation region 406includes an electrode support member 408 which provides support for aplurality of electrically isolated electrode terminals 410 (see FIG. 5).As shown, support member 408 includes a central lumen 424 foraccommodating a pacemaker lead 66 (see FIG. 9) so that the lead 66 onlypasses through support member 408 (i.e., the entire catheter shaft 402does not have to be advanced over the lead 66). This design shouldfacilitate the advancement of the catheter 60 over the lead.

In the embodiment shown in FIGS. 4-7, catheter 60 includes a singlereturn electrode 422 for completing the current path between electrodeterminals 410 and high frequency power supply 80 (see FIG. 3). As shown,return electrode 422 preferably comprises an annular conductive bandcoupled to the distal end of shaft 402 slightly proximal electrodesupport member 408, typically about 0.5 to 20 mm and more preferablyabout 1 to 10 mm. Return electrode 422 is coupled to a connector (notshown) that extends to handle 404, where it is suitably connected topower supply 80, as discussed above.

As shown in FIG. 4, return electrode 422 is not directly connected toelectrode terminals 410. To complete this current path so that electrodeterminals 410 are electrically connected to return electrode 422,electrically conducting fluid (e.g., isotonic saline, electricallyconductive gel, or an electrically conductive gas) is caused to flowtherebetween. In the representative embodiment, the electricallyconducting fluid is delivered through a fluid tube 412 to an opening atthe distal end 420 of catheter shaft 402. Fluid tube 412 extends throughan opening in handle 404, and includes a connector 414 for connection toa fluid supply source, for supplying electrically conductive fluid tothe target site. Depending on the configuration of the distal ablationregion 406, fluid tube 412 may extend through a single lumen (not shown)in shaft 401, or it may be coupled to a plurality of lumens (also notshown) that extend through shaft 402. In the representative embodiment,the fluid lumen(s) have openings (not shown) at the distal end 420 ofthe catheter shaft 402 to discharge the electrically conductive fluidproximal to return electrode 422 and electrode terminals 410. However,the lumens may extends through to support member 408, if desired.Catheter 400 may also include a valve (not shown) or equivalentstructure for controlling the flow rate of the electrically conductingfluid to the target site.

In alternative embodiments, the fluid path may be formed in catheter 400by, for example, an inner lumen or an annular gap between the returnelectrode and a s tubular support member within shaft 402. This annulargap may be formed near the perimeter of the shaft 402 such that theelectrically conducting fluid tends to flow radially inward towards thetarget site, or it may be formed towards the center of shaft 402 so thatthe fluid flows radially outward. In other embodiments, the fluid may bedelivered by a fluid delivery element (not shown) that is separate fromcatheter 60. A more complete description of an electrosurgicalinstrument incorporating one or more fluid lumen(s) can be found inparent application Ser. No. 08/485,219, filed on Jun. 7, 1995, thecomplete disclosure of which has previously been incorporated herein byreference.

Referring to FIG. 5, the electrically isolated electrode terminals 410are spaced apart over a distal tissue treatment surface 430 of electrodesupport member 408. The tissue treatment surface 430 and individualelectrode terminals 410 will usually have dimensions within the rangesset forth above. In the representative embodiment, the tissue treatmentsurface 430 has an circular cross-sectional shape with a diameter in therange of 1 mm to 20 mm, preferably about 1 to 5 mm. The individualelectrode terminals 410 preferably extend outward from tissue treatmentsurface 430 by a distance of about 0.05 to 4 mm, usually about 0.1 to 1mm.

In the embodiment of FIGS. 4-7, the catheter includes a single, largeropening 424 in the center of tissue treatment surface 430, and aplurality of electrode terminals (e.g., about 3-30) around the perimeterof surface 430. Alternatively, the catheter 60 may include a single,annular, or partially annular, electrode terminal at the perimeter ofthe tissue treatment surface. The central lumen 424 (or a peripherallumen) may be coupled to a suction lumen (not shown) within shaft 402for aspirating tissue, fluids and/or gases from the target site.Aspirating the electrically conductive fluid during surgery allows thesurgeon to see the target site, and it prevents the fluid from flowinginto the patient's body, e.g., into the heart or lung.

Handle 404 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 404 defines aninner cavity that houses the electrical connections (not shown), andprovides a suitable interface for connection to an electrical connectingcable (see FIG. 1). A more complete description of an exemplary handleand associated electrical connections can be found in co-pending U.S.patent application entitled “Systems and Methods for Endoscopic SinusSurgery”, filed Dec. 15, 1997, the complete disclosure of which isincorporated herein by reference.

Referring now to FIGS. 6 and 7, an exemplary flex circuit 440 forelectrically coupling electrode terminals 410 to the catheter body 402will now be described. As shown, flex circuit 440 includes a pluralityof flexible wires 442 (e.g., copper wires) coupling electrode terminals410 to a plurality of connectors 444 on catheter shaft 402, which aresuitably coupled to wires or other electrical connectors that extendthrough shaft 402 to handle 404. Flex circuit 440 preferably comprises aflexible material, such as polymide, that can be deformed such thatwires 442 extend from each of the electrode terminals 410 surroundinglumen 424 of support member 408 to one side of support member 408, andthen back to a semi-circular configuration within catheter shaft 408.This design ensures that the wires 442 do not interfere with thepacemaker lead 66 (FIG. 9) that extends through lumen 424 as the supportmember 408 is advanced over the lead.

Of course, it should be recognized that other configurations arepossible. For example, the catheter shaft 402 may have the same or alarger diameter as support member 408 so that central lumen 424 ofsupport member 408 abuts against the catheter shaft 402. In thisconfiguration, shaft 402 will have also have a central lumen alignedwith lumen 424 for accommodating the pacemaker lead through a portion orall of the shaft. In one embodiment (see FIG. 15), for example, thecatheter shaft 402 may have a slit or opening disposed proximal tosupport member 408 that allows pacemaker lead to be fed through the slitand the internal lumen, similar to the embodiment described above. Inthis embodiment, a flex circuit may not be desirable or necessary.

Referring not to FIGS. 8-12, a second embodiment of a catheter accordingto the present invention will now be described. As shown in FIG. 8,catheter body 62 has an internal lumen 68 sized to accommodate apacemaker lead 66 (see FIG. 9), as described above. In this embodiment,internal lumen 68 extends from a distal opening 69 (see FIG. 8A) to theproximal end 70 of catheter body 62 (FIG. 10) so that the pacemaker lead66 acts as the guidewire for advancing the distal end of the catheter tothe target site. Of course, a separate guidewire (not shown) may be usedto guide distal ablation region 64 of catheter 60 to the target site. Inparticular, for other applications, such as removing tissue ingrownaround a the distal end of catheter 60 to the stent. For the removal ofpacemaker leads, however, applicant has found that it is advantageous touse the lead as the guidewire because the distal end of catheter 60 isalready positioned to remove the fibrous scar tissue between the heartwall and the lead.

As shown in FIG. 8A, the distal ablation region 64 of catheter body 62includes first and second electrode assemblies 72, 74 extending beyondthe distal opening 69 of the central lumen 68. Of course, it will berecognized that the catheter may include more or less than two electrodeassemblies (e.g., see FIGS. 16-21). Electrode assemblies 72, 74 stent orstent-graft within a body lumen, for example, a guidewire may beutilized to guide each include an active electrode terminal 76 extendingfrom an electrically insulating support member 78. Electrode terminals76 preferably comprise an electrically conductive metal or alloy, suchas platinum, titanium, tantalum, tungsten, stainless steel, gold,copper, nickel and the like. The electrode terminals 76 should besufficiently long to extend the “coring” depth of the terminals 76during the ablation/cutting operation to at least 0.5 mm, usually atleast 2 mm, preferably at least 5 mm.

In addition, electrode terminals 76 preferably an active portion orsurface having a surface geometry shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a PHless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode. A more complete description of suitable electrodegeometries can be found in U.S. application Ser. No. 08/687792, filed onJul. 18, 1996, previously incorporated herein by reference.

In the representative embodiment, electrode terminals 76 preferablycomprise electrode wires which are flattened at their tips 80 (e.g., inthe shape of a screwdriver tip) to provide a more rapid tissueablation/cutting action (see FIG. 12). The support members 78 comprisean inorganic insulator, such as ceramic, glass, glass/ceramic or a highresistivity material, such as silicon or the like. An inorganic materialis generally preferred for the construction of the support members 78since organic or silicone based polymers are known to rapidly erodeduring sustained periods of the application of high voltages betweenelectrodes terminals 76 and the return electrode 120 during tissueablation. However, for situations in which the total cumulative time ofapplied power is less than about one minute, organic or silicone basedpolymers may be used without significant erosion and loss of material ofthe support members 78 and, therefore, without significant reduction inablation performance.

In the embodiment shown in FIG. 8A, catheter 60 includes a single returnelectrode 120 for completing the current path between electrodeterminals 76 and power supply 80 (see FIG. 3). As shown, returnelectrode 120 preferably comprises an annular conductive band at thedistal end of catheter 60 slightly proximal to electrode supportmembers. Return electrode 90 is spaced from electrode terminals 76 asufficient distance from the electrode terminals 76 to substantiallyavoid or minimize current shorting therebetween and to shield the returnelectrode 120 from tissue at the target site, usually about 0.5 to 10 mmand more preferably about 1 to 10 mm. Return electrode 120 is coupled toa connector (not shown) that extends to the proximal end of catheter 60,where it is suitably connected to power supply 80 by connector 89, asdescribed above in connection with FIG. 3.

In the embodiment shown in FIG. 8B, catheter 60 includes a pair ofreturn electrodes 122, 124 located on electrode assemblies 72, 74proximal to the support members 78. As in the above embodiment, returnelectrodes 122, 124 are spaced from electrode terminals 76 a sufficientdistance to substantially avoid or minimize current shortingtherebetween and to shield the return electrodes 122, 124 from tissue atthe target site. This embodiment has the advantage that the electriccurrents are substantially confined to a region that is distal to thedistal end of catheter body 62, which facilitates advancement of thecatheter body 60 through fibrous scar tissue.

Both embodiments (FIGS. 8A and 8B) include a pair of fluid lumens 126,128 for delivering electrically conductive fluid, e.g., isotonic salineor argon gas, to the electrode terminals 76, and a pair of suctionlumens 130, 132 for aspirating fluids and/or tissue fragments from thetarget site. The fluid lumens 126, 128 extend through catheter body 62to fluid tube 103 (see FIG. 3). The electrically conductive fluidprovides a current flow path between electrode terminals 76 and thereturn electrodes 120, 122, 124. In addition, the fluid is one of therequisites for establishing the Coblation™ mechanism of the presentinvention, as discussed above. Alternatively or additionally, the body'snaturally conductive fluids (e.g., blood) may be used for these purposesdepending on the location of the implanted object (e.g., a stent locatedwithin a blood vessel). The suction lumens 130, 132 also extend throughcatheter body 62 to a source of vacuum (not shown) for aspiratinggaseous products of ablation and/or tissue fragments from the targetsite. In addition, the suction lumens 130, 132 may be used to aspirateexcess electrically conductive fluid from the target site, if, forexample, a high flow rate of this fluid is necessary for the procedure.

Catheter body 62 preferably includes reinforcing fibers or braids (notshown) in the walls of at least the distal ablation region 64 of body 62to provide responsive torque control for rotation of electrode terminals76 during tissue engagement. This rigid portion of the catheter body 62preferably extends only about 7 to 10 mm while the remainder of thecatheter body 62 is flexible to provide good trackability duringadvancement and positioning of the electrodes 74, 76 adjacent to thepacemaker lead 66.

As an alternative to the irrigation lumens shown in FIGS. 8-12, theirrigant or electrically conductive fluid may be supplied through thelumen 140 of tubular electrodes 142 (see FIG. 13) in place of theshaped, solid wires shown in FIGS. 8-12. This may be advantageous inensuring that electrically conductive fluid is injected into closeproximity to the site of tissue ablation/cutting. Further, the tubingcan be filed as shown in FIG. 13 to expose additional edges 144 toenhance the tissue cutting effect.

During the percutaneous introduction and removal of catheter body 62,measures should be taken to prevent iatrogenic injury to the walls ofthe vessels and heart as well as the valves and other tissuesencountered along the pathway to the target site, viz., the embeddedportion of the pacemaker lead tip. In the embodiment shown, in FIGS. 14Aand 14B, catheter 60 includes a compliant, atraumatic safety sheath 170which extends over electrode assemblies 72, 74. Safety sheath 170 has adistal opening 172 for accommodating lead 66, and comprises a compliantmaterial that will allow sheath to retract over catheter body 64, asshown in FIG. 14A. In use, sheath 170 is advanced forward as shown inFIG. 14A during introduction and removal of tissue ablation region 64.Once the target site has been accessed, the compliant, atraumatic safetysheath 170 is retracted (e.g., a distance of 1.5 to 2.0 cm) exposingelectrode assemblies 72, 74. Once the ablation of an annular channel inthe tissue surrounding the pacemaker lead tip 66 is complete, the safetysheath 170 can be displaced forward to cover the distal portion ofablation region 64.

The safety sheath 170 is preferably constructed using thin-walledplastic tubing selected to provide biocompatability, compliance and lowfriction during insertion and removal. A number of plastic materials areavailable for this purpose and include Teflon, polypropylene andpolyvinyl chloride. The activation mechanism may be (1) the thin-walledplastic tubing moved relative to the catheter body at a locationexternal to the patient's body or (2) a drive rod or wire (not shown)within the catheter body which actuates a short segment of the safetysheath (e.g., 4 to 8 cm) located at the distal end of the catheter body.

Another embodiment of the present invention is shown in FIG. 15. In thisembodiment, catheter body 62 includes a lateral or side port 150 at ornear tissue ablation region 64. As shown, lateral port 150 is coupled tocentral lumen 68, and allows the distal end portion of the catheter 60to be advanced over the pacemaker lead 66 without having to extend thelead 66 through the entire length of the catheter 60. This facilitatesthe procedure and typically shortens the amount of time required toadvance electrode terminals 160 along the lead 66. The side port 150 maybe formed in the catheter body 62 proximal to electrically insulatingmember 162 as shown in FIG. 15, or it may be formed directly in theinsulating member 162.

In the embodiment of FIG. 15, electrode terminals 160 are spaced aroundthe periphery of a ceramic insulating support member 162. In addition,support member 162 may include one or more holes 164 for delivering ofelectrically conductive fluid and/or for aspirating the target site.Alternatively, aspiration and/or fluid delivery may be accomplishedthrough central lumen 68. As shown in FIG. 15, electrode terminals 76are substantially flush with the distal surface of support member 162.This configuration minimizes the current flux density around theelectrode terminals 160 because they have no sharp edges or corners,thereby reducing the rate of tissue ablation. In some cases, applicanthas found that this allows a slower and more controlled rate of tissueremoval. For fibrous scar tissue around pacemaker leads, however, thesharper, exposed electrode terminals 76 of previous embodiments may bepreferred. As shown, electrode terminals 160 each have a flat tape wire166 that extends through insulating support member 162, and throughcatheter body 62 to the proximal end thereof.

Another embodiment of tissue ablation region 64 of catheter 60 is shownin FIGS. 16A and 16B. As shown, two active electrodes 180 a, 180 b aresecured within an electrically insulating support member 182. Thesupport member 182 is secured to the distal end of catheter 60 with abiocompatible adhesive 183 between support member 182 and outer sleeve184 of catheter 60. A central lumen 186 in support member 182 provides apassageway for pacemaker lead 66 that permits axial displacement androtation of tissue ablating region 64 relative to lead 66. An irrigationlumen 188 and an aspiration lumen 190 are also provided to injectelectrically conducting fluid and to remove gaseous products of ablationfrom the target site.

The return electrode (not shown) comprises an annular electrode on thecatheter body proximal to support member 182. Alternatively, the returnelectrode may be located within central lumen 186 proximal of theexposed portion of active electrodes 180 a, 180 b. In this embodiment,the electric currents are confined to a region between active electrodes180 a, 180 b and central lumen 186, which may further limit currentpenetration into the surrounding heart wall.

In use with the present invention, catheter 60 is rotated as theelectrodes 180 a, 180 b are energized by generator 80 (FIG. 3) to effectablation of the tissue attached to lead 66. Preferably, a reciprocatingrotational motion is employed, combined with a small pressure to advancetissue ablation region 64 through the longitudinal length of the scartissue to detach the pacemaker lead 66 from the heart wall. Thecross-sectional shape of the active electrodes 180 a, 180 b may be roundwires as shown in FIG. 16B, or they may have shaped surfaces to enhancethe electric field intensity at the distal surfaces of the activeelectrodes, as discussed above.

FIGS. 17-21 illustrate other embodiments of tissue ablation region 64 ofcatheter 60 according to the present invention. In FIGS. 17A and 17B,for example, four active electrodes 190 are secured within an inorganicelectrically insulating support member 182. The cross-sectional shape ofthe active electrodes 190 may be round wires as shown in FIG. 17B, orthey may have shaped surfaces to enhance the electric field intensity atthe distal surfaces of the active electrodes as described. Anotherembodiment of tissue ablation region 64, illustrated in FIGS. 18A and18B, includes a single active electrode 192 secured within supportmember 182 . As before, electrode 192 is preferably rotated as theregion 64 is advanced through the scar tissue.

FIGS. 19A and 19B illustrate an embodiment with six active electrodes194 secured within inorganic support member 182. An annular irrigationlumen 196 and an aspiration lumen 198 are provided to injectelectrically conducting fluid 199 and remove gaseous products ofablation 201 from the target site. The return electrode 200 (FIG. 19B)in this embodiment is positioned within the catheter 60 aroundirrigation lumen 196. As shown, return electrode 200 is an annularelectrode that may extend over a portion, or the entire length, ofirrigation lumen 196. In this embodiment, it may not be necessary ordesirable to rotate the catheter 60 relative to the pacemaker lead 66.

Referring to FIGS. 20A and 20B, yet another embodiment of the inventionincludes a single active electrode 210 comprising a coiled wire having aplurality of concentric coils 212 tightly and helically wrapped andsecured on support member 182 (FIG. 20B). Preferably, the helical coilextends around a return electrode 214 in. concentric configuration, asshown in FIG. 20A. Another embodiment of the invention is shown in FIGS.21A and 21B. This embodiment is similar to the above embodiment exceptthat the single active electrode 216 defines a series of concentricmachined grooves 218 to form concentric circular electrodes 222surrounding a return electrode 220. The distal edges of electrodesgenerate regions of high electric field intensities when high frequencyvoltage is applied between return electrode 220 and concentric activeelectrodes 222. A vapor layer 224 forms at and around active electrodes222 with concomitant volumetric removal (ablation) of the scar tissue orocclusive media. The embodiments of FIGS. 20 and 21 are usually advancedthrough the fibrous scar tissue or occlusive media without rotation.

Referring now to FIGS. 22-24, methods for removing implanted pacemakerleads from a patient's venous system and heart will now be described. Asshown in FIG. 22, a typical transvenous endocardial lead 300 connects apacemaker 302 to the heart H through the right subclavian vein S, andsuperior vena cava C and down into the heart H. Transvenous endocardiallead 300 is shown specifically in the right ventricle V, although leadsto the right atrium A are often used as well. The distal end of lead 300includes an electrode 306 for electrically stimulating the heart and aplurality of tines 308 to provide fixation of lead 300 within heart H.As discussed above, during chronic implantation, the lead 300 becomesaffixed along its side surfaces to inner surfaces of the venous systemand at its distal end to heart H through the formation of fibrous scartissue T.

In use, the proximal end of lead 300 is uncovered surgically andintroduced into the central guide lumen 68 of catheter 60 (see FIG. 8).Once catheter 60 is positioned so lead 300 extends into guide lumen 68,the catheter 60 is advanced until distal end 64 of catheter 60 isproximate the fibrous scar tissue T. FIG. 24 illustrates an embodimentin which the lead 300 extends through the entire length of catheter 60.However, it should be clearly understood that the catheter 60 mayincorporate a side port near its distal end as described above to allowfor a more rapid exchange of the catheter over the pacemaker lead 66.Once the surgeon has reached the point of blockage, electricallyconductive fluid is delivered through fluid lumens 126, 128 to thetissue (see FIG. 8A). The rate of fluid flow is controlled with valve 17(FIG. 1) such that the zone between the tissue and electrode terminals76 is constantly immersed in the fluid. The power supply 80 is thenturned on and adjusted such that a high frequency voltage difference isapplied between electrode terminals 76 and return electrode 120. Theelectrically conductive fluid provides the conduction path (see currentflux lines) between electrode terminals 76 and the return electrode 120.

FIG. 23 illustrates the removal of scar tissue T around the lead 66 inmore detail As shown, the high frequency voltage is sufficient toconvert the electrically conductive fluid 310 between the target tissueT and electrode terminal(s) 76 into an ionized vapor layer or plasma(not shown). As a result of the applied voltage difference betweenelectrode terminal(s) 76 and the target tissue T (i.e., the voltagegradient across the plasma layer), charged particles in the plasma(viz., electrons) are accelerated towards the tissue. At sufficientlyhigh voltage differences, these charged particles gain sufficient energyto cause dissociation of the molecular bonds within tissue structures.This molecular dissociation is accompanied by the volumetric removal(i.e, ablative sublimation) of tissue and the production of lowmolecular weight gases 314, such as oxygen, nitrogen, carbon dioxide,hydrogen and methane. The short range of the accelerated chargedparticles within the tissue confines the molecular dissociation processto the surface layer to minimize damage and necrosis to the surroundingtissue.

During the process, the gases 314 may be aspirated through suctionlumens 130, 132 to a vacuum source. In addition, excess electricallyconductive fluid, other fluids (e.g., blood), or non-ablated tissuefragments may be aspirated from the target site to facilitate thesurgeon's view and to prevent these tissue fragments or the excess fluidfrom flowing into the patient's heart or vasculature. During ablation ofthe tissue, the residual heat generated by the current flux lines(typically less than 150° C.), will usually be sufficient to coagulateany severed blood vessels at the site. If not, the surgeon may switchthe power supply 80 into the coagulation mode by lowering the voltage toa level below the threshold for fluid vaporization, as discussed above.This simultaneous hemostasis results in less bleeding and facilitatesthe surgeon's ability to perform the procedure.

As the scar tissue is ablated, the catheter 60 is rotated relative tothe lead 66 such that an annular channel of tissue is ablated. Thecatheter 60 is then advanced through the scar tissue as it ablates thistissue until the lead is released. Catheter 60 is repositioned untilonce again the distal end is proximate fibrous scar tissue. Applicationof high frequency electrical energy to electrode terminals is repeatedalong the entire length of lead 66 until lead is not longer affixed byfibrous scar tissue along its side surface. The voltage will typicallybe applied continuously during the ablation of a section of tissue.However, the heartbeat may be monitored and the voltage applied inpulses that are suitably timed with the contractions (systole) of theheart.

Once the side surface of lead 66 is released from the fibrous scartissue T, only fibrous scar tissue proximate distal end of lead 66 atdistal face of electrode retains the lead, as shown in FIG. 24. At thispoint, the electrode terminals 76 may be used to ablate through tines308, particularly if tines 308 are constructed from common leadmaterials, such as silicone or polyurethane. Alternatively, electrodeassemblies may be deflected radially outward so that the electrodeterminals 76 cut or ablate around the tines 308 of the lead tip 306. Inother embodiments, the lead 300 may be severed proximal to the tip 306,and the tip 306 left within the heart tissue. In yet other embodiments,traction may be applied to either the proximal end of lead, or to pointproximal the tip, such as through a snagging stylet as disclosed in U.S.Pat. Nos. 5,207,683, 5,013,310, and 4,988,347, to withdraw lead fromfibrous scar tissue T. Use may also be made of a sheath, as described inU.S. Pat. No. 5,011,482 to Goode et al., to overlay the lead duringtraction and apply counter traction at a site near the electrode toconfine the traction force to an area within the sheath.

The principles of the present invention are also applicable to any bodylumen which becomes partially or totally occluded. For example, thepresent invention is useful in a lumen containing a lumenal prosthesis,such as a stent, stent-graft or graft, which may be metallic,non-metallic or a non-metallic coated metallic structure. A particularadvantage of the present invention is the confinement of current flowpaths (not shown) between the return electrode (hollow guide wire in thepresent example) and one or more active electrodes to the vicinity oftissue ablating region of the catheter. This confinement of current flowpaths minimizes the undesired flow of current through portions or all ofthe stent, which may otherwise induce non-specific tissue injury beyondthe site of recanalization of the occluded lumen. A more completedescription of methods and apparatus for ablating occlusive media withinbody lumens can be found in commonly assigned, co-pending U.S.application Ser. No. 08/874,173 entitled “SYSTEMS AND METHODS FORELECTROSURGICAL RESTENOSIS OF BODY LUMENS”, filed Jun. 13, 1997, thecomplete disclosure of which is incorporated herein by reference for allpurposes.

What is claimed is:
 1. An apparatus for removing a pacemaker lead attached to heart tissue within a patient's body comprising: a shaft having a proximal end, a distal end, a distal opening and an inner lumen in communication with the distal opening, the distal opening and the inner lumen being sized to accommodate the pacemaker lead; an electrode terminal on the shaft adjacent the distal opening; an electrically insulating support member at the distal end of the shaft supporting the electrode terminal, the support member comprising an inorganic material selected from the group comprising ceramic, glass or combinations thereof; and a connector extending from the electrode terminal to the proximal end of the shaft for coupling the electrode terminal to a source of high frequency electrical energy.
 2. The apparatus of claim 1 wherein the inner lumen extends from the distal opening to the proximal end of the shaft.
 3. The apparatus of claim 1 further comprising a hole in the shaft spaced proximally from the distal opening and sized to accommodate the pacemaker lead, the inner lumen extending from the distal opening to the hole.
 4. The apparatus of claim 3 wherein the hole is spaced about 0.1 to about 10 cm from the distal opening of the shaft.
 5. The apparatus of claim 1 further comprising a return electrode on the shaft spaced from the electrode terminal.
 6. The apparatus of claim 1 further comprising a plurality of electrically isolated electrode terminals circumferentially spaced around the distal opening of the shaft.
 7. The method of claims 1 wherein the electrically insulating support member has a distal opening aligned with the distal opening of the shaft, and a proximal opening spaced from the distal opening and sized to accommodate the pacemaker lead, wherein the inner lumen couples the proximal and distal openings.
 8. The apparatus of claim 1 further comprising a plurality of electrically isolated electrode assemblies extending distally from the distal end of the shaft and circumferentially spaced around the distal opening, each of the electrode assemblies comprising an active electrode, an electrically insulating support member coupled to the active electrode and a return electrode positioned proximal to the active electrode and the support member.
 9. The apparatus of claim 1 wherein the electrically insulating support member comprises a distal tissue treatment surface, and the electrode terminal is substantially flush with the tissue treatment surface.
 10. The apparatus of claim 1 wherein the electrically insulating support member comprises a distal tissue treatment surface, and the electrode terminal extends from the tissue treatment surface by a distance of less than 3 mm.
 11. The apparatus of claim 1 further comprising one or more suction lumens within the shaft, each having a distal opening at the distal end of the shaft, and a proximal end adapted for coupling to a vacuum source.
 12. The apparatus of claim 1 further comprising at least one fluid lumen within the shaft having a distal opening at the distal end of the shaft, and a proximal end adapted for coupling to a source of electrically conductive fluid for delivering electrically conductive fluid to a region around the electrode terminal.
 13. The apparatus of claim 12 wherein the fluid lumen is positioned so as to deliver electrically conductive fluid past a return electrode and the electrode terminal to generate a current flow path therebetween.
 14. The apparatus of claim 12 wherein the fluid lumen extends through the electrode terminal.
 15. The apparatus of claim 1 wherein the electrode terminal has a flattened distal end.
 16. The apparatus of claim 1 wherein the electrode terminal extends from the distal end of the shaft about 0.05 to 5 mm.
 17. The apparatus of claim 1 wherein the shaft has a length of about 50 to 80 cm.
 18. The apparatus of claim 1 wherein the inner lumen of the shaft has a diameter of about 0.5 to about 10 mm.
 19. A method for removing a pacemaker lead attached to heart tissue within a patient's body comprising: positioning a plurality of electrically isolated electrode terminals adjacent a portion of the pacemaker lead attached to the heart tissue; applying high frequency voltage to the electrically isolated electrode terminals and at least one return electrode in the presence of electrically conductive fluid such that an electrical current flows from each of the electrode terminals, through the electrically conductive fluid, and to the return electrode, the high frequency voltage being sufficient to detach said portion of the pacemaker lead from the heart tissue; and independently controlling current flow from at least two of the electrode terminals based on impedance between each of the electrode terminals and the return electrode.
 20. The method of claim 19 further comprising advancing a distal portion of a catheter body over the pacemaker lead to position the electrode terminals in close proximity with the tissue attached to the lead.
 21. The method of claim 20 wherein the electrode terminals are positioned at a distal portion of the catheter body, the method further comprising rotating at least the distal portion of the catheter body during the applying step.
 22. The method of claim 20 wherein the catheter body has an inner lumen sized to accommodate the pacemaker lead, the method further comprising advancing the catheter body over the length of the pacemaker lead to position the electrode terminals adjacent the heart tissue attached to the lead.
 23. The method of claim 19 further comprising applying a sufficient high frequency voltage difference between one or more of the electrode terminals and the return electrode to ablate a portion of the heart tissue attached to the pacemaker lead and further advancing the electrode terminals along the pacemaker lead as the heart tissue releases the lead.
 24. The method of claim 19 wherein the return electrode is proximal to the electrode terminals such that the electrical current flows from the electrode terminals in a proximal direction to the return electrode away from the tissue.
 25. The method of claim 19 further comprising aspirating a region around the electrode terminals.
 26. The method of claim 19 wherein the high frequency voltage is sufficient to vaporize the fluid in a thin layer between at least a portion of the electrode terminals and the heart tissue.
 27. The method of claim 26 further comprising accelerating charged particles from the vaporized fluid to the heart tissue to cause dissociation of the molecular bonds within the heart tissue.
 28. The method of claim 19 further comprising directing an electrically conductive fluid through a fluid lumen in a catheter body to the electrode terminals to generate a current flow path between the electrodes terminal and the return electrode.
 29. The method of claim 19 wherein the pacemaker lead includes a distal tip embedded within heart tissue, the method further comprising removing the distal tip of the pacemaker lead from the heart tissue by applying sufficient high frequency voltage to one or more of the electrode terminals to remove at least a portion of the tissue surrounding the tip.
 30. The method of claim 29 further comprising deflecting the electrode terminals radially outward to accommodate an enlarged distal tip of the pacemaker lead.
 31. The method of claim 29 wherein the distal tip of the pacemaker lead includes one or more tines extending radially outward from the lead, the method further comprising severing the tines. catheter body over the length of the pacemaker lead to position the electrode terminal adjacent the heart tissue attached to the lead.
 32. The method of claim 19 wherein the electrode terminals are located on a distal portion of a catheter body having an inner lumen, a distal hole and an opening in the catheter body proximal to the distal hole, the method further comprising advancing the distal portion of the catheter body over the length of the pacemaker lead such that the lead extends through the distal hole, the inner lumen and the proximal opening.
 33. A method for removing a pacemaker lead attached to heart tissue within a patient's body comprising: positioning an electrode terminal adjacent a portion of the pacemaker lead attached to the heart tissue, wherein the pacemaker lead includes a distal tip embedded within the heart tissue and having one or more tines extending radially outward from the lead; applying a first high frequency voltage to the electrode terminal to detach said portion of the pacemaker lead from the heart tissue; and removing the distal tip of the pacemaker lead from the heart tissue by applying a second high frequency voltage to the electrode terminal to remove at least a portion of the tissue surrounding the tip and sever the tines.
 34. The method of claim 33 further comprising advancing a distal portion of a catheter body over the pacemaker lead to position the electrode terminal in close proximity with the tissue attached to the lead.
 35. The method of claim 34 further comprising aspirating a region around the electrode terminal.
 36. The method of claim 34 wherein the first and second high frequency voltages are sufficient to vaporize an electrically conductive fluid in a thin layer between at least a portion of the electrode terminal and the heart tissue.
 37. The method of claim 36 further comprising accelerating charged particles from the vaporized fluid to the heart tissue to cause dissociation of the molecular bonds within the heart tissue.
 38. The method of claim 34 wherein the catheter body has an inner lumen sized to accommodate the pacemaker lead, the method further comprising advancing the catheter body over the length of the pacemaker lead to position the electrode terminal adjacent the heart tissue attached to the lead.
 39. The method of claim 34 wherein the electrode terminal is located on a distal portion of a catheter body having an inner lumen, a distal hole and an opening in the catheter body proximal to the distal hole, the method further comprising advancing the distal portion of the catheter body over the length of the pacemaker lead such that the lead extends through the distal hole, the inner lumen and the proximal opening.
 40. The method of claim 33 wherein the first high frequency voltage is sufficient to to ablate a portion of the heart tissue attached to the pacemaker lead, the method further comprising further advancing the electrode terminal along the pacemaker lead as the heart tissue releases the lead.
 41. The method of claim 33 wherein the first and second high frequency voltages are applied between the electrode terminal and a return electrode, and wherein the return electrode is proximal to the electrode terminal such that an electrical current flows from the electrode terminal in a proximal direction to the return electrode away from the tissue.
 42. The method of claim 33 wherein the electrode terminal is positioned at a distal portion of a catheter body, the method further comprising rotating at least the distal portion of the catheter body during the applying step.
 43. The method of claim 33 further comprising directing an electrically conductive fluid through a fluid lumen in a catheter body to the electrode terminal to generate a current flow path between the electrode terminal and a return electrode. 